A Wavelength-Division-Multiplexed (WDM) transmission link often includes multiple segments of transmission fiber separated by one or more optical amplifiers and other fiber optic components. Generally speaking, it is desirable that these links exhibit uniform signal transmission for all wavelengths. Unfortunately however, non-uniformity in gain and loss accumulate and eventually cause transmission errors unless the signal is equalized.
Such equalization in wavelength division multiplexed systems may be achieved by a variety of means including signal pre-emphasis, fixed fiber gratings, and individual attenuators placed between wavelength routers. Each of these approaches represents a tradeoff in network operator flexibility.
An approach to WDM equalization was described by the inventors of the present application in U.S. patent application Ser. No. 08/690,696 filed on Jul. 31, 1996 for an Attenuation Device For Wavelength Multiplexed Optical Fiber Communications and is incorporated herein by reference. This previous approach, involved multiple wavelength signals in an optical fiber spatially dispersed by wavelength over a row of voltage-controlled variable reflectivity modulators in which reflected (and attenuated) signals are combined into a single optical output fiber. Despite advantages of this technique, a continuing need exists in the art for equalization apparatus and techniques that provide enhanced optical performance.